Surface characterization of metal nanoparticles

Air exposed aluminum and nickel nanoparticles were investigated using high-resolution and analytical transmission electron microscopy (HREM/AEM), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). The diameter of the Al particles ranged from 20 to 260 nm with an average size of 100±50 nm. Individual Ni particles were spherical, ranging from 7 to 230 nm in size with an average size of 70±45 nm. The Al nanoparticles were covered by a 3 nm thick amorphous and compact surface oxide layer. Ni nanoparticles were surrounded by a non-uniform, crystalline surface oxide layer. Elemental analysis indicated that the Al nanoparticles contained O and Si and that the oxygen is associated with the particle surface layer, while no oxygen confinement in the surface layer was found in Ni nanoparticles. XPS confirmed the NiO presence in the surface layer of Ni particles. These results suggest that the sintering behavior of these metal nanoparticles may be inhibited, though to a different degree, due to the surface oxides.